72 



MOUNTING AND LABELING. 



on. The cover-glass is warmed slightly also, both to make it stick to 

 the cell more easily, and to expel any remaining moisture from the ob- 

 ject. When the cover is put on it is pressed down all around over the 

 cell until a shining ring appears, showing that there is an intimate con- 

 tact. In doing this use the convex part of the fine forceps or some 

 other blunt, smooth object ; it is also necessary to avoid pressing on the 

 cover except immediately over the wall of the cell for fear of breaking 

 the cover. When the cover is in contact with the wall of cement all 

 around, the slide should be placed on the turn-table and carefully ar- 

 ranged so that the cover-glass and cell wall will be concentric with the 

 guide rings of the turn-table. Then the turn-table is whirled and a 

 ring of fresh cement is painted, half on the cover and half on the cell 

 wall (Fig. 40). If the cover-glass is not in contact with the cell wall at 

 any point and the cell is shallow, there will be great danger of the fresh 

 cement running into the cell and injuring or spoiling the preparation. 



When the cover-glass is properly sealed, the preparation is put in some 

 safe place for the drying of the cement. It is advisable to add a fresh 

 coat of cement occasionally. 



(B) Thick or deep cells. These may be made of paper, sheet lead or 

 block tin, etc. They should be slightly deeper than the object to be 

 mounted is thick. It is sometimes advisable to have a circular opening 

 and an oblong wall instead of using a mere ring. In any case the cell 

 wall is cemented to the slide and the cement well dried before use. If 

 the cell is for dry objects or for those in glycerin, a ring of fresh cement 

 is added just before putting on the cover-glass. If glycerin jelly, a res- 

 inous substance, or Farrant's solution is to be used as the mounting 

 medium no cement on the top is necessary. 



§ 169. Sealing the Cover-Glass when no Cell is Used. — (A) 

 For glycerin mounted specimens. The superfluous glycerin is wiped 

 away as carefully as possible with a moist cloth, then four minute drops 

 of cement are placed at the edge of the cover (PI. V, Fig. 50), and 

 allowed to harden for half an hour or more. These will anchor the 

 cover-glass, then the preparation may be put on the turn-table and a ring 

 of cement put around the edge while whirling the turn-table. 



(B) For objects in glycerin jelly, Farrant's solution or a resinous me- 

 dium. The mounting medium is first allowed to harden, then the su- 

 perfluous medium is scraped away as much as possible with a knife, and 

 then removed with a cloth moistened with water for the glycerin jelly 

 and Farrant's solution or with alcohol, chloroform or turpentine, etc., 

 if a resinous medium is used. Then the slide is put on a turn-table and 

 a ring of the shellac cement added. (C) Balsam preparations may be 

 sealed with shellac as soon as they are prepared, but it is better to al- 

 low them to dry for a few days. One should never use a cement for 



